DivinDriver

iTrader: (15)

Oh, the upper governor shaft... The parts fiche don't give a separate part # for it; part of the governor set. Includes the mech advance and the whole shaft

On the 79 & 80, part # 8341-24-330
On the 81, part # N249-24-330 (12A's)

That makes it inconclusive in re: swapping, as it could be only the advance curves, the springs, or one of a dozen parts in the assembly that changed. Or the shaft.

Reluctor (with roll pin):
80: 8245-24-316
81: 8248-24-316

Definitely it changed. No telling from this by how much.

If you do, that'd be outstanding. Measure across the major diameter of the reluctor, too; possible it got larger to close the gap on the pickups, or something. Hate to have it fit on the shaft but whack into the pickups!

I'll go down and measure mine, too... if I get 'round tuits.

Using shielded cable would work real good, too... that's what Mazda did on the '80, for the same reason.

snwyvern

I like where this thread is going. My fourteen cents: the signal the 81+ distributor put out on the o-scope @ 18k rpm was steady and had the "heartbeat"-/+ signal that the GM HEI likes to see (http://www.megamanual.com/ms2/GM_7pinHEI.htm). It was a 2 channel scope, so the leading and the trailing pickups matched in shape without stepping on each other. (That's good, I can't give you a voltage +/- at a given RPM, a cordless high-speed drill was used to spin the dizzy shaft.)

In the interest of... data gathering... does anybody know what the advance curves for the mechanical and vac. advance(s) are? As you (all) have probably gathered, I will eventually use a modified TFIDFIS (Wasted spark, amirite?) with the GM 7-pin Ignitors with advanced timing being controlled by a MS2 board.

Also: Is there a range of set-gap plugs that are... cheap... I considered getting some Autolite 2592s/2594s to test gap-settings before getting another set of (wider than BUR7EQ) NGKs, but... I'm flying blind on this one. Does anyone have any input?

DivinDriver

iTrader: (15)

What were you seeing as pk-pk voltage change on the 81?

t_g_farrell

iTrader: (1)

Heres a pic of the 80 vs 85 reluctor. Note the 85 has a significant change in
shape and will generate a different signal wave form. I think you should be able
to adjust the air gap to accomodate the newer reluctor.



and heres the 85 reluctor:

arghx

iTrader: (3)

I believe that's for an '80 model, not sure how much it differs.

you'll have to figure out a plug that will have the stock heat range. Most people switching away from surface discharge plugs are using a 10-11 heat range, for which there are multiple options.

DivinDriver

iTrader: (15)

"Significant" doesn't say half of it... the entire curvature is reversed! I thought at first one of the pictures had been transposed, but no... the pickup coils and magnets are positioned the same. The curvature of the FB reluctor is opposite that of the SA.

My experience with the SA pickup plate assembly is that it's not possible to adjust the gaps in any real sense; gap position is maintained by crimp-reinforced bends in formed steel plates of around 1/8" thickness. Trying to adjust them by bending with an accuracy of thousandths would be well-nigh impossible.

FSM states that when the air gap is out of spec, the entire pickup assembly must be replaced.

Jeff20B

iTrader: (13)

Round part of '81 shaft: 17.91mm
flat section: 16.36mm

snwyvern

The waveform would stay the same, but the voltage was dependant on the speed of the input... I can put it on the scope one more time before putting on on the car this evening? This was a little difficult because of the scaling required to get the waveforms on screen... I'll see if I can catch a video.


I'm mostly concerned with having some baseline to test the theory that the TFIDFIS setup or Jeff's setup pumps out a "hotter spark/more voltage spark/better spark" if that's true, a wider gap can be used along with the timing and air/fuel goodies to take advantage of that. Traditional plugs that fit (such as the Autolite previously mentioned) can be widened-out, but I want(ed) to try and stick with a quality plug. From NGK's naming scheme, I should be looking for a BUR7EQ-20, but... It seems that that part doesn't exist. Meh.

Glazedham42

iTrader: (4)

Check out this spark plug thread. It may give you some good ideas on what plugs you want to experiment around with. It starts out pretty basic, but by page 3 you're getting into some pretty detailed information. Hyper's posts are especially helpful.

https://www.rx7club.com/1st-generation-specific-1979-1985-18/whats-best-spark-plugs-165434/

Jamie

j9fd3s

iTrader: (3)

Mazda was nice enough to put them in the FSM's. they do vary slightly 79-80, 81-82, 83, and 84-85

to tell which one you have, you can look on the body of the distributor, there is a 4 digit number, under the mistubishi number. N201, N304, etc etc

if you get that number and look it up in the parts catalog it'll be there.

n201 is 81-82
n231 is 83
n249 is 84-85 12a
n304 is 84-85 gsl-se

snwyvern

Thanks. I had to download the "High Res" chapter on ignition to draw out anything legible out of the tables that are in the FSM. The difference(s) between the mechanical advances aren't that important, only so much as to get into a ballpark to start using MS2's fine tuning... And to setup the GM 7-Pins to do the same.

j9fd3s

iTrader: (3)

agreed. the early cars have the advance come on a tad quicker, but if i remember correctly the 84-85's have more total timing

DivinDriver

iTrader: (15)

OK, here are the shaft numbers from my SA dizzy:

Shaft diameter: 17.89mm
Flat spot diameter: 16.50mm

Close enough to Jeff's measurements to be margin-of-error.

The reluctor outside diameter, across the outermost points, is 35.95mm

Reluctor design:

j9fd3s

iTrader: (3)

it that looks almost the same as the FB one, i wonder if the wheel alone swaps over?

the other thing to look at would be the 2 seals, and the dizzy gear, if those are the same SA to FB then the whole shaft assembly should be a drop in

DivinDriver

iTrader: (15)

The key things would be:

1) the phase angle between the index point on the dizzy and the reluctor arms. In other words, is there the same number of rotational degrees between the center of the "flat spot" and the tips of the reluctor. That angle dictates firing timing.

Looking at these pics you posted:

80 reluctor


85 reluctor:


You can see that on the 85, there's a tip of the reluctor that's lined up almost exactly over the center of the shaft flat spot. On the 80, the tip seems offset from the center of the flat by several degrees.



2) the reversed shape of the reluctor seems like it would reverse the waveform of the output pulse. The SA reluctor looks to set up for a sharp initial wavefront, tapering off, whereas the FB reluctor seems designed for a tapering lead-up with a sharp break-off. Makes me wonder if the electronics in the ignitors aren't designed to trigger differently.

The SA electronic ignition has more electronics in it than the FB does; in the SA, the signal from the pickups goes through a pre-amplifier in the fender-mounted box the ignitors attach to, on the FB the ignitors are connected directly to the pickup coils. Might be the pre-amp inverts the signal waveform or does other electronic shenanigans before the signal hits the ignitor.

t_g_farrell

iTrader: (1)

This is exactly why I think the HEI failed with the SA dizzy and works great with
the FB dizzy. I can only offer my experiences in my write up as proof. You may be
right that the SA ignitor box electronics play a role.

You can hide some HEIs in that box instead maybe